Pressure responsive potentiometers



March 10, 1959 M.. E. BOURNS PRESSURE RESPONSIVE POTENTIOMETERS Filed March 30. 1955 2,877,326 Patented Mar. 10, 1959 fie 2,877,326 PRESSURE RESPONSIV E PGTENTIOMETERS Marian E. Bourns, Riverside, Calif. Application March 30, 1955, Serial No. 497,876 13 Claims. ('Ql. 201-48) The present invention relates primarily to new and improved pressure responsive potentiometers.

it is well known to those skilled in the art to which this invention pertains that there is a continuing need for accurate, reliable pressure responsive potentiometers which can be employed in missile and other applications at a Wide range of temperatures without loss of accuracy. In the past much pressure responsive potentiometers have been frequently manufactured so as to utilize either a Bourdon tube or one or more bellows so that as such means are subjected to higher pressures they expand causing various mechanical linkages to be actuated in changing an electrical value. These prior constructions have thus been limited by the fact that it was necessary to employ various means linking the pressure responsive tube or bellows employed with the actual electrical component in order to multiply mechanically the movement of the pressure responsive means so as to obtain a sufiicient variation in the adjustment of the electrical component for practical purposes.

it is an object of this disclosure to teach the construction of pressure responsive electrical instruments such as potentiometers in which the various complicated linkages frequently encountered in the prior art devices are replaced by a single member directly secured to an extremity of a Bourdon tube. Thus, this invention is aimed at producing pressure responsive electrical instruments which are simpler than prior constructions of like accuracy and effectiveness.

It is also an objective of this invention to provide end terminals for resistance elements employed in potentiometers, these end terminals being responsive to changes in temperature so as to change locations with respect to resistance elements at different temperatures. This type of construction is exceedingly advantageous inasmuch as the end terminals referred to can be constructed sothat the effective length of a resistance element measured in terms of its electrical resistance remains constant regardless of the temperatures under which such resistance element is operated. This is frequently very important when materials are employed for resistance elements which have appreciable temperature coefficients of resistance. For practical reasons it is frequently desired to use such materials for resistance elements. Also, temperature responsive end terminals as herein described are advantageous inasmuch as they can be constructed so as to compensate for diflerences in the spring rate of Bourdon tubes at different temperatures.

It is also an object of this invention to provide new and improved pressure responsive adjustable resistors such as potentiometers which are accurate, reliable, and which are capable of standing at great deal of rough treatment. Further objects of this invention as well as many advantages of it will be apparent from the remainder of this specification including the appended claims and the accompanying drawings in which:

Fig. l is a cross-sectional view of a pressure responsive,

temperature compensated potentiometer of the invention taken at line 1-1 of Fig. 2;

Fig. 2 is a cross-sectional view taken at line 2-2 of Fig. 1;

Fig. 3 is a view similar to Fig. 1 of a modified potentiometer of the invention taken at line 3-3 of Fig. 4;

Fig. 4 is a cross-sectional view taken at line 4-4 of Fig. 3 of the drawings;

Fig. 5 is a view similar to Fig. 3 of a second modified potentiometer of the invention taken at line 5-5 of Fig. 6;

Fig. 6 is a cross-sectional view taken at line 6-6 of Fig. 5; and

Fig. 7 is a detail view showing the construction of a bimetallic strip employed with the invention.

In all figures of the drawings like numerals have been employed to designate like parts wherever practical. It is to be understood that the instant invention is not limited to constructions employing various parts having the proportional sizes shown in the drawings inasmuch as the proportional sizes of certain of the parts have been changed for convenience of illustration and explanation.

This invention is primarily concerned with pressure responsive, temperature compensated instruments of the class described which include: a spiral Bourdon tube; an inlet for admitting fluid under pressure to said tube; means movably mounting an extremity of said tube remote from said inlet; contact means operatively secured to said extremity of said tube; electrical resistance means mounted adjacent to said contact means so that during the introduction of fluid under pressure into said tube said contact means is moved along said resistance means; and terminal means contacting said resistance means, said terminal means being capable of moving with respect to said resistance means as the temperature of said terminal means is changed.

A summary of this category must be explainedwith reference to the drawings illustrating the invention if the true nature of the invention is to be completely explained. In Figs. 1 and 2 of the drawings a pressure responsive, temperature compensating potentiometer 10 is shown which includes a body member in the form of a generally cylindrical can-like casing 12 having an open end 14 and a closed end 16. Within the center of this closed end 16 there is positioned a small opening 18 through which fluid, such as, for example, air under pressure may be introduced into the interior of a Bourdon tube 20. This tube as is secured to the closed end 16 around the opening l8= by the use of a mounting block 22. It is considered obvious that this tube 20 is attached. to the mounting block 22 by conventional means such as, for example, solder. A tapped fitting 24 may be secured about the opening 18 to the closed end 16 so that the fluid conveyed to the Bourdon tube 20 may come from an appropriate air line or the like. i

The precise nature of the Bourdon tube 20 is quite important with the instant invention. This tube is formed so as to have comparatively thin flexible walls which may, if desired, be made out of any common metal such as brass. This tube is flattened and twisted throughout its length so as to normally assume aspiral shape such as is shown in Fig. 1 of the drawings. Be; cause of this shape when fluid under pressureis introduced into the tube 20 through the opening l8 the tube tends to unwind about the axis of this spiral so as to tend to assume a straight sheet-like configuration. vIn practice this configuration is never achieved. The rotation of the Bourdon tube 20 during expansion as described in the preceding is controlled through the use of a small shaft 26 secured, as by soldering, to a inovable end 28 of the Bourdon tube 20. This movable 3 end is, of course, the end of the Bourdon tube remote from the closed end 16. The shaft 26 fits Within an opening 30 formed in a non-conductive disc-like mounting bracket 32 secured within the casing 12 so as to be parallel to the closed end 16 through the use of screws 34. Preferably this mounting bracket 32 is formed of such material as nylon or various filled phenolic resins so that the walls of the opening 30 are in and of themselves capable as serving as a bearing carrying the shaft 26. If desired, however, various conventional bearing means may be located so as to be attached to the mounting bracket 32 in order to accomplish the same purpose.

Within the mounting bracket 32 there is formed an arcuate opening 36 in which there is disposed a conventional resistance element 38. This element 38 projects from both sides of this mounting bracket 32. Conven tional means such as, for example, an adhesive are utilized so as to maintain the position of this resistance element. A resilient contact arm 40 is secured to the movable end 28 of the Bourdon tube 20 adjacent to the shaft 26 in such a manner that during rotation of this shaft the contact arm 40 is moved along the resistance element 38 engaging different portions of this resistance element 38.

On the side of the mounting bracket 32 remote from the tube 20 terminal elements 42 are mounted so as to slidably engage the resistance element 38. Each of these terminal elements 42 comprises a screw 44 secured to the mounting bracket 32, a spiral bimetallic strip 46 welded or otherwise rigidly connected to the screw 44 and a short wiper arm 48 attached to the spiral strip so as to resiliently bear against the resistance element 38. The precise construction of the spiral strips 46 is best indicated in Fig. 7 of the drawings where it is shown that these strips are composed of two layers 50 and 52 respectively of difierent metals or metal alloys having different temperature coeflicients of expansion.

Wires 54 are passed through openings 56 within an end disc 58 which is secured to the open end 14 of the casing 12 by screws 34. These wires 54 are employed to connect the terminal elements 42 and the contact arm 40 into an electrical circuit. Two of these wires are secured to the screws 44, and a third is passed through another opening 57 in the mounting bracket 32 and is secured to an extremity 60 of the contact arm 40 for the obvious purpose. The extremity 60 serves an additional function of balancing the weight of the contact arm 40 on opposed sides of the shaft 26 in order to prevent binding of this shaft.

The operation of the potentiometer 10 is considered to be essentially obvious from the aforegoing description. As fluid under pressure is introduced into the Bourdon tube 20 the contact arm 40 is rotated so as to engage different portions of the resistance element 38. Undesired movement of the Bourdon tube 20 which might result from such items as vibration is controlled because of the shaft 26 so that the contact arm 40 always moves in exactly the desired path.

As the potentiometer 10 is subjected to increasing temperaturesthe spiral strip 46 tend to expand more or less uncoiling in shape with the result that the wiper arms 48 are moved along the resistance element 38 so that the efiective distance between these two wiper arms is correlated with the temperature of the potentiometer 10. Thus with this type of construction it is possible to manufacture potentiometers in which the effective resistance between the terminal elements 42 remains constant regardless of the temperature coefiicient of the resistance element employed.

In Figs. 3 and 4 of the drawings a modified potentiometer 62 of the invention is shown which includes a body member in the form of a can-like cylindrical casing 64 having an open end 14 and a closed end 16. Within the open end 14 there is located a non-conductive closure 66 which is preferably formed of a dielectric resinous material such as, for example, a filled phenolic resin, nylon, or the like. This closure is secured to the easing 64 through the use of screws 34. It includes a projecting boss 68 having a threaded opening 70 formed therein. This threaded opening 70 is adapted to be connected to a pressure tube in the same manner as the tapped opening 24.

Within the opening 70 there is located a shoulder 72 against which there is held a metal tube 74 having a closed end 76. This closed end 76 is secured to a nonround shaft 78 by appropriate means such as, for example, welding. The shaft 78 is normally positioned within a non-round socket 80 located on the closed end E6 of the casing 64 in such a manner that rotation of the tube 74 is prevented. This tube has formed therein adjacent to the closed end 76 a side opening 82 within which there is located an end of a spiral Bourdon tube 84. The end of this Bourdon tube 84 remote from the tube 74 carries a resilient contact arm 86 which is secured to the Bourdon tube 84 by appropriate means such as, for example, welding. A small projecting stabilizing shaft 88 is similarly secured to this same end of the Bourdon tube 84 so as to project from the tube 84 into an arcuate groove 90 formed on the closed end 16 of the casing 64.

During the operation of the potentiometer 62 fluid such as air under pressure travels through the opening 70 into the Bourdon tube 84 causing this tube to expand. This expansion results in what may be termed unwinding of the tube 84. As such unwinding occurs the stabilizing shaft 88 slides within the groove 90 guiding the contact arm 86 in an arcuate path about the tube 84 so that this contact arm 86 moves against a resistance layer 92 located upon the closure 66 in a path corresponding to the shape of the groove 90. Because of this construction the potentiometer 62 is substantially immune to the effects of vibration. The inherent resiliency of the contact arm 86 maintains the shaft 88 within the groove 90 at all times. Further, the position of both ends of the Bourdon tube 84 is maintained as desired.

The temperature compensating effects are obtained in the potentiometer 62 through the use of bowed bimetallic terminal element strips 94 which are secured to screws 44 in the same manner as the spiral strips 46 are secured to the screws 44 previously described. To the ends of each of the strips 94 there are attached wiper arms 48 of the same category as previously described. The position of the screws 44 and the strips 94 is such that the wiper arms 48 are at all times in contact with the resistance layer 92 within the normal temperature range in which the potentiometer 62 is designed to operate.

In Figs. 5 and 6 of the drawings a second modified potentiometer 96 of the invention is shown as including a can-like cylindrical casing 98 having a closed end 16 and an open end 14. Within the side of this casing 98 there is located, as by welding or the like, a fitting 100 having a tapped opening 102 projecting therethrough so that an appropriate airline or the like may be connected to this fitting 100 in order to transmit pressure from an appropriate source into a Bourdon tube 104, an end of which is secured, as by welding or the like, in a side opening 106 in the fitting 100 leading to a tapped opening 102.

The end of the spiral Bourdon tube 104 remote from the fitting 100 is rigidly secured to a shaft 108 carried between an opening 110 in a non-conductive closure 112 which is secured to the casing 98 by means of screws 34 and a round socket 114 secured to the closed end 16 of the casing 98. Thus with this construction the shaft 108 is free to rotate during expansion or contraction of the Bourbon tube 104 as fluid, such as air, is introduced to or removed from this Bourdon tube. If desired various conventional bearing means such as ball or roller bearings can be used to hold the shaft 108.

Attached to the shaft 108 is a radially projecting rod 116 which is preferably formed of a nonconductive material of the type such as previously indicated. Secured to this rod 116 is a contact member 118 having two resilient wiper arms 120 secured thereto. These wiper arms 126 are arranged in such a manner that one of them is designed to move against an arcuate strip 122 of relatively high electrical conductance secured to the closure 112. The other of these wiper arms 120 is designed to ride along another arcuate strip 124 of a resistance composition placed upon the closure 112. Thus, with this construction, because of the inherent resiliency of these wiper arms 120, electrical conductance is established through the contact member 118 between the strips 122 and 124.

Mounted upon each of two terminal boltsv 13th are terminal elements in the form of two bowed bimetallic strips 126 the ends of which are secured together; The ends of the strips 126 remote from the bolts 130 are secured to wiper arms 128 which are designed to bear against the ends of the strip 124. The strips 126 are secured to the bolts 130 in the same manner in which the spiral strips 46 were secured to the screws 44 previously described. With this construction, as the temperature of the strips 126 increases the wiper arms 128 move along the resistance element strip 124 so as to vary the effective distance between these two wiper arms with the same result previously indicated. The terminal bolts 130 projecting: through openings 132 in. theclosure 112 so that they may be used to connect the strips 126 and the wiper arms 128 into an electrical circuit. Similarly another bolt 131 having formed therein a short contact arm 134 may be used to connect strip 122 to an electrical circuit.

Those skilled in the art will realize that a great many modifications may be made in the constructions shown without departing from the true scope of this invention. As an example of such modifications, the terminal elements shown with any of the potentiometers illustrated may be substituted for any of the other terminal elements described. Also, various minor refinements essentially of an engineering nature may be employed so as to alter the units shown for commercial production. Those skilled in the art will further realize that the contact arms or terminal elements shown connected to the extremities of the resistance element can be employed with other than pressure responsive potentiometers as herein described. The application of temperature responsive end terminals with pressure responsive potentiometers is, however, particularly advantageous since such temperature responsive end terminals, when constructed in any of the manners indicated in this specification, or in equivalent ways, can be so found to compensate for the change in spring rate of the pressure responsive means employed. This is important in the production of extremely accurate instruments. All modifications of the invention which are within the skill of the art and the scope of the appended claims are to be considered as part of the inventive concept.

I claim:

1, A pressure responsive, temperature compensated instrument of the class described which includes: a Bourdon tube having one end thereof fixed and the other end movable; an inlet for admitting fluid into said one end of said tube; contact means operatively secured to said movable end of said tube; electrical resistance means mounted adjacent to said contact means so that during the introduction of fluid into said tube said contact means is moved along said resistance means; and temperature responsive terminal elements contacting said resistance means, said terminal elements being operable to engage ditferent portions of saidresistance means as the temperature of said terminal elements is changed.

2. An instrument as defined in claim 1 wherein said terminal elements include'a spiral bimetallic strip.

3. An instrument as defined in claim 1 wherein said terminal elements include a bowed bimetallic strip.

4. An instrument as defined in claim 1 wherein said terminal elements include two bowed bimetallic strips, the ends of said strips being secured together.

5. An instrument as defined in claim 1 wherein said Bourdon tube is twisted along an axis.

6. An instrument as defined in claim 1' wherein said Bourdon tube is spiral in shape, and wherein said means for controlling the motion of said movable end of said Bourbon tube comprises a shaft-rotatably mounted within said housing.

7. A pressure responsive,. temperature compensated electrical instrument which includes: a housing; a Bourdon tubehaving anend rigidly'secured within said housing and having a movable'end located within said housing; means defining an inlet in said housing for admitting fluid into said end rigidly secured within said housing; means for controlling the movement of said movable end located within said housing; contact means operatively secured to said movable end; anelectrical resistance element mounted within said housing adjacent to said con tact means so as to be engaged thereby during movement of said movable end; and terminal elements having contacts engaging at least one end of Said resistance element, said terminal elements being operable to engage difierent portions of saidresistance element as the temperature of said terminal means is changed.

8. A pressure responsive, temperature compensated. electrical instrument which includes: a housing; a Bourdon tube having an end rigidly secured within said housing and having a movable end located within said housing; meansdefining an inlet-in saidvhousing for admitting fluid into said end rigidly secured within said housing; contact means operatively secured to said movable end; a resistance element mounted within said housing adjacent to said contact means so as to be engaged thereby during movement of said movable end; a bimetallic strip mounted within said housing adjacent to said resistance element, said bimetallic strip having a movable end capable of movement as the temperature of said strip is changed; and a wiper arm attached to said movable end of said strip so as to engage said electrical resistance element, said wiper arm being capable of movement along said resistance element so as to engage different portions of said resistance element as the temperature of said strip is changed.

9. A pressure responsive, temperature compensated electrical instrument which includes: a housing; a curved Bourdon tube having an end rigidly secured within said housing and having a movable end located Within said housing; mitting fluid into said end rigidly secured within said housing; means for controlling the movement of said movable end located within said housing; contact means operatively secured to said movable end; a resistance element mounted within said housing adjacent to said contact means so as to be engaged thereby during movement of said movable end; and terminal elements engaging at least one end of said resistance element, each of said terminal elements comprising a curved bimetal strip, one end of said strip being mounted in a fixed position and the other end of said strip being movable, and a wiper arm engaging said electrical resistance element attached to said movable end of said strip whereby as the temperature of said strip is changed said wiper arm is moved so as to engage different portions of said resistance element.

10. A pressure responsive, temperature compensated potentiometer which includes: a housing; a spiral Bourdon tube having an end rigidly secured within said housmeans defining an inlet in said housing for ad- I ing and having a movable end located within said housing; means defining an inlet in said housing for admitting fluid into said end rigidly secured within said housing; means for controlling the movement of said movable end located within said housing; contact means secured to said movable end so as to project therefrom; a resistance element mounted Within said housing adjacent to said contact means so as to be engaged thereby during movement of said movable end; and terminal elements engaging opposite extremities of said resistance element, each of said terminal elements including a bowed bimetal strip, one of said ends of said strip being secured against movement and the other end of said strip being movable and a wiper arm attached to said movable end of said strip, said Wiper arm engaging said electrical resistance element at an extremity thereof so that as the temperature of said strip is changed said wiper arm is moved so as to engage different portions of said resistance element.

11. A pressure responsive, temperature compensated potentiometer which includes: a housing; a spiral Bourdon tube having one end at the center of the spiral rigidly secured within said housing and the other end thereof being movable; means defining an inlet in said housing for admitting fluid into said center end; contact means secured to said movable end of said Bourdon tube so as to project therefrom; a resistance element mounted within said housing adjacent to said contact means so as to be engaged thereby during movement of said movable end; means defining a groove within said housing; a stabilizing shaft fixed to the movable end of said Bourdon tube and projecting into said groove; and therminal elements engaging the ends of said resistance element, each of said terminal elements including a bowed bimetal strip having ends, one of said ends of said strip being secured against movement and the other of said ends of said strip being movable and being located adjacent to said resistance element, and a wiper arm attached to said movable end of said strip so as to engage an end of said resistance element whereby as the temperature of said strip is changed said wiper arm is moved with respect to said resistance element so as to engage different portions thereof.

12. A pressure responsive, temperature compensated instrument of the class described which includes: a pressure responsive member having a fixed end and a movable end, contact means operatively secured to said movable end of said pressure responsive member, an electrical resistance element mounted adjacent to said contact means so that during movement of said movable end in response to pressure said contact means is moved with respect to said electrical resistance element, and terminal elements contacting said resistance element, said terminal elements being operable to engage different portions of said resistance element as the temperature of said terminal means is changed.

13. A potentiometer which includes: an electrical resistance element, terminal elements engaging the ends of said resistance element, said terminal elements being temperature responsive so as to be capable of movement so as to engage different portions of the ends of said resistance element as the temperature of said potentiometer is changed, and electrical contacts mounted on said terminal elements to engage said resistance element, said contacts being movable so that the relative portions of said contacts on said resistance element with respect to one another are capable of being changed.

References Cited in the file of this patent UNITED STATES PATENTS 2,226,629 Mather Dec. 31, 1940 2,264,487 Smulski Dec. 2, 1941 2,286,717 Clason June 16, 1942 2,622,177 Klose Dec. 16, 1952 

